ESX vs. ESXi

Capability	VMware ESX	VMware ESXi
Service Console	Service Console is a standard Linux environment through which a user has privileged access to the VMware ESX kernel. This Linux-based privileged access allows you to manage your environment by installing agents and drivers and executing scripts and other Linux-environment code.	VMware ESXi is designed to make the server a computing appliance. Accordingly, VMware ESXi behaves more like firmware than traditional software. To provide hardware-like security and reliability, VMware ESXi does not support a privileged access environment like the Service Console for management of VMware ESXi. To enable interaction with agents, VMware has provisioned CIM Providers through which monitoring and management tasks – traditionally done through Service Console agents – can be performed. VMware has provided remote scripting environments such as vCLI and PowerCLI to allow the remote execution of scripts.
CLI-Based Configuration	VMware ESX Service Console has a host CLI through which VMware ESX can be configured. VMware ESX can also be configured using vSphere CLI (vCLI).	The vSphere CLI (vCLI) is a remote scripting environment that interacts with VMware ESXi hosts to enable host configuration through scripts or specific commands. It replicates nearly all the equivalent COS commands for configuring ESX. Notes:   vCLI is limited to read-only access for the free version of VMware ESXi. To enable full functionality of vCLI on a VMware ESXi host, the host must be licensed with vSphere Essentials, vSphere Essential Plus, vSphere Standard, vSphere Advanced, vSphere Enterprise, or vSphere Enterprise Plus.   VMware vSphere PowerCLI (for Windows) and vSphere SDK for Perl access ESXi through the same API as vCLI. Similarly, these toolkits are limited to read-only access for the free version of VMware ESXi. When the host is upgraded to vSphere Essentials, vSphere Essential Plus, vSphere Standard, vSphere Advanced, vSphere Enterprise, or vSphere Enterprise Plus these toolkits have write-access and provide a scriptable method for managing ESXi hosts. Certain COS commands have not been implemented in the vCLI because they pertain to the management of the COS itself and not ESXi. For details,
Scriptable Installation	VMware ESX supports scriptable installations through utilities like KickStart.	VMware ESXi Installable does not support scriptable installations in the manner ESX does, at this time. VMware ESXi does provide support for post installation configuration script using vCLI-based configuration scripts.
Boot from SAN	VMware ESX supports boot from SAN. Booting from SAN requires one dedicated LUN per server.	VMware ESXi may be deployed as an embedded hypervisor or installed on a hard disk.   In most enterprise settings, VMware ESXi is deployed as an embedded hypervisor directly on the server. This operational model does not require any local storage and no SAN booting is required because the hypervisor image is directly on the server. The installable version of VMware ESXi does not support booting from SAN.
Serial Cable Connectivity	VMware ESX supports interaction through direct-attached serial cable to the VMware ESX host.	VMware ESXi does not support interaction through direct-attached serial cable to the VMware ESXi host at this time.
SNMP	VMware ESX supports SNMP.	VMware ESXi supports SNMP when licensed with vSphere Essentials, vSphere Essential Plus, vSphere Standard, vSphere Advanced, vSphere Enterprise, or vSphere Enterprise Plus. The free version of VMware ESXi does not support SNMP.
Active Directory Integration	VMware ESX supports Active Directory integration through third-party agents installed on the Service Console.	VMware ESXi does not support Active Directory authentication of local users at this time.
HW Instrumentation	Service Console agents provide a range of HW instrumentation on VMware ESX.	VMware ESXi provides HW instrumentation through CIM Providers. Standards-based CIM Providers are distributed with all versions of VMware ESXi. VMware partners include their own proprietary CIM Providers in customized versions of VMware ESXi. These customized versions are available either from VMware’s web site or the partner’s web site, depending on the partner.    Remote console applications like Dell DRAC, HP iLO, IBM RSA, and FSC iRMC S2 are supported with ESXi.
Software Patches and Updates	VMware ESX software patches and upgrades behave like traditional Linux based patches and upgrades. The installation of a software patch or upgrade may require multiple system boots as the patch or upgrade may have dependencies on previous patches or upgrades.	VMware ESXi patches and updates behave like firmware patches and updates. Any given patch or update is all-inclusive of previous patches and updates. That is, installing patch version “n” includes all updates included in patch versions n-1, n-2, and so forth.  Furthermore, third party components such as OEM CIM providers can be updated independently of the base ESXi component, and vice versa.
VI Web Access	VMware ESX supports managing your virtual machines through VI Web Access. You can use the VI Web Access to connect directly to the ESX host or to the VMware Infrastructure Client.	VMware ESXi does not support web access at this time.
Licensing	For licensing information, see the VMware Sphere Editions Comparison.	For licensing information, see the VMware Sphere Editions Comparison.
Diagnostics and Troubleshooting	VMware ESX Service Console can be used to issue commands that can help diagnose and repair support issues with the server.	VMware ESXi has several ways to enable support of the product: Remote command sets such as the vCLI include diagnostic commands such as vmkfstools, resxtop, and vmware-cmd. The console interface of VMware ESXi (known as the DCUI or Direct Console User Interface) has functionality to help repair the system, including restarting of all management agents. Tech Support Mode, which allows low-level access to the system so that advanced diagnostic commands can be issues. For more information,
Jumbo Frames	VMware ESX 4.0 fully supports Jumbo Frames.	VMware ESXi 4.0 fully supports Jumbo Frames.